Pokemon Red/Blue versions came out in North America on Sept. 28, 1998. In the game, the main character is on a mission to catch fictional creatures named Pokemon, which stands for Pocket Monsters. There was originally 151 pokemon at the time and they came in many different varieties. Some of the most common types were grass, water, fire, flying, and psychic. Each type has it strengths and weaknesses, making Pokemon a strategic game in which trainers try to catch pokemon of various types. Basically the game plays like an rpg, allowing trainers to carry up to 6 pokemon with them at any given time. Pokemon get stronger through experience and level up starting at level 1 with the maximum being level 100. Throughout the game, you battle against other trainers, gym leaders, your rival, and eventually the Elite 4. The game was quite revolutionary at the time and became an instant classic.
Here is a short video showing some classic gameplay of the original game: